In general, a fluid viscosity measuring device configured to measure the viscosity of a fluid such as blood is referred to as a viscometer. Kinds of viscometers widely used so far include a capillary viscometer, a rotary viscometer, etc. However, typical viscometers such as a capillary viscometer or a rotary viscometer have problems in that the consumption amount (approximately a milliliter) of a sample is relatively high, a great deal of measurement time (approximately 1 hour) is required, and measurement errors are relatively frequent. On the other hand, a microfluidic device-based viscometer has advantages such as a relatively small consumption amount (approximately a microliter) of a sample, a short measurement time (approximately several minutes), and accurate real-time evaluation of repetitiveness and reproducibility, and thus its research has been widely conducted. Such a microfluidic viscometer is essentially required to analyze accurate rheological properties. In particular, the microfluidic viscometer is considered to be one of analytic tools in the field of applications such as chemistry, biology and biomedical engineering. There is an increasing demand for equipment that can rapidly and accurately measure viscosity due to the necessity and availability of the microfluidic viscometer.
To measure the viscosity of a target fluid using a microfluidic device, various methods using a pressure drop due to friction loss caused by fluid flow of a target fluid have been proposed. The methods proposed in the related art are classified into two groups: “a) a method of directly measuring viscosity using a pressure sensor, and b) a method of indirectly measuring viscosity using a change in boundary surface according to a viscosity ratio between two fluids. First, the method of directly measuring viscosity using a pressure sensor essentially requires complicated calibration and correction. On the other hand, the method of indirectly measuring viscosity using a change in boundary surface according to a viscosity ratio between two fluids can be used to easily measure viscosity without using a pressure sensor. However, since the shape of the boundary surface may be widely changed according to the viscosity ratio or a surface tension ratio between two fluids, such a method requires calibration and correction to accurately detect the boundary surface of the target fluid, and requires image processing as well.